In U.S. Pat. No. 4,234,069 issued on Nov. 18, 1980 to the assignee of the present application, there is disclosed apparatus for controlling the speed of vehicles on trackways. In one specific embodiment, the apparatus comprises a pair of wheels mounted on an axle for combined rotary and axial motion in a frame which carries brake pads outboard of the wheels. A pair of these assemblies may be mounted to the underside of a pallet for riding on one or more inclined rails mounted in a storage rack. The assemblies control the speed of the pallet on the rail by causing the load on the pallet to urge the wheels outwardly into engagement with the brake pads for creating friction between the wheels and the frame and thereby slowing the speed of the vehicle as it advances down the rails.
While the aforementioned patented invention operates entirely satisfactorily for its intended purpose to control the speed of a vehicle on an inclined trackway, there is a demand for a speed control device which can be used in conjunction with highly flexible members, such as cables, ropes, chains, etc. to lower loads vertically or at steep inclines at controlled rates of speed from a higher level to a lower level. For instance, one application for the invention includes fire escape devices where it is necessary for a person to be able to lower himself from a high level to a lower level at a controlled safe rate of speed. Another application for the invention is in providing a controlled rate of descent for a platform in an elevator in the event the main drive for the elevator should fail. In all of these applications, there is a need for a device which provides accurate speed control, which is highly reliable in operation, and which has a minimum of moving parts so as to be capable of being manufactured economically by high speed mass production techniques.